Tumor Necrosis Factor, or more specifically Tumor Necrosis Factor-alpha, is a cytokine, primarily produced by stimulated macrophages, that exhibits not only a striking cytotoxicity against various tumour cells [Carswell et al., Procd. Nat. Acad. Sci., U.S.A. 72, 3666-3670, (1975)] but also plays a multiple role as a mediator of inflammation and the immune response [See Beutler and Cerami, Ann. Rev. Immunol. 7, 625-655 (1989); Bonavista and Granger (eds.) "Tumor Necrosis Factor: Structure, Mechanism of Action, Role in Disease and Therapy", Karger, Basel (1990)]. The primary structure of human Tumor Necrosis Factor-alpha (hTNF-.alpha.) has been deduced from the nucleotide sequence of a cDNA which has been cloned and expressed in E. coli [Pennica et al., Nature 912, 724-729 (1984); Marmenout et al., Europ. J. Biochem. 152, 515-522 (1985); Wang et al., Science 228, 149-154 (1985); Shirai et al., Nature 313, 803-806 (1985)]. A striking homology in amino acid sequence (30%) was found between hTNF-.alpha. and human Lymphotoxin, often referred to as human Tumor Necrosis Factor-beta (hTNF-.beta.), a cytokine produced by a subset of lymphocytes [Gray et al., Nature 312, 721-724 (1984); Fiers et al., Cold Spring Harbour Symp. 51, 587-595 (1986)].
hTNF-.alpha. with modified amino acid sequences, so called TNF-.alpha.-muteins, have also been described in the art [See, e.g., Yamagishi et al., Protein Engineering 3, 713-719, (1990) or by Fiers in "Tumor Necrosis Factors: Structure, Function and Mechanism of Action", Aggarwal and Vilcek (eds.), Marcel Dekker, Inc., New York, (in press), or by Fiers et al. in Bonavista and Granger, pp. 77-81 Supra. In addition TNF-.alpha.-muteins have also been the object of several patent applications, for example, International Patent Applications Publ. Nos. WO 86/02381, WO 86/04606, WO 88/06625 and European Patent Applications Publ. Nos. 155,549; 158,286; 168,214; 251,037 and 340,333, and Deutsche Offenlegungsschrift Nr. 3843534.
Muteins of Lymphotoxin have also been disclosed in the art, for example in European Patent Applications Publ. Nos. 250,000; 314,094 and 336,383.
The biological effects of TNF are mediated via specific receptors, namely a receptor with an apparent molecular weight of 55 kD on sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) (p55-TNF-R) and a receptor with an apparent molecular weight of 75 kD on SDS-PAGE (p75-TNF-R). Both forms of TNF-receptors have been cloned previously. The cloning of p55-TNF-R was done by Loetscher et al. [Cell 61, 351-359, (1990)] and the cloning of p75-TNF-R was done by Dembic et al. [Cytokine 2, 53-58, (1990)] See also European Patent Application No. 90116707.2 (both receptors). It was found more recently that both receptors bind not only TNF-.alpha., but also TNF-.beta. with high affinity [Schonfeld et al., J. Biol. Chem. 266, 3863-3869 (1991)].